Power generation with rankine cycle engines using alkylated adamantanes as a working fluid

ABSTRACT

Adamantanes having lower alkyl bridgehead substitutents can be used as working fluids in Rankine cycle engines, and particularly in small vapor turbine systems.

United States Patent Bechtold et al. 1 Mar. 14, i972 [54] POWER GENERATION WITH RANKINE 260/666 M; 60/36 CYCLE ENGINES USING ALKYLATED ADAMANTANES AS A WORKlNG [561 References Cited FLU") UNITED STATES PATENTS [72] Inventors: Max Fredrick Bechtold, Kennett Square; 2 4 2 B l 60 36 Charles William Tullock, Landenberg, g izgi x338 Y 60136 both of Pa.

[73] Assignee: E. l. du Pont de Nemours and Company, Primary Examiner-Leon D. Rosdol Wilmington, Del. Assistant Examiner-Harris A. Pitlick [22] Filed: Aug. 17, 1970 Attorney-D. R. J. Boyd [2]] Appl. N0.: 64,222 [57] ABSTRACT Adamantanes having lower alkyl bridgehead substitutents can [52] [1.8. CI ..60/36, 252/67, 252/73, b d as working fluids in Rankine cycle engines, and par- 260/666 M ticularly in small vapor turbine systems. [51] Int. Cl. ..F01k 25/00, C09k 3/02 [58] Field of Search ..252/67-69, 73; 5 Claims, 2 Drawing Figures TEMPERATURE C CONDENSATION l3 ENTROPY FATENTEDMAR 14 1972 HEAT " BOILER POWER PUMP CONDENSER Fl G- 2- SATURATED LIQUID LINE |4 CONDENSATION l3 ENTROPY INVENTORS MAX FREDRICK BECHTOLD CHARLES WILLIAM TULLOCK BY @MLY ATTORNEY POWER GENERATION WITll-ll RANllfllNllE CYCLE ENGllNlES USING ALKYLATED AIDAMANTANKES AS A WORKING lFLiJllll) BACKGROUND OF THE lNVENTlON 1. Field of the Invention This invention relates to Rankine cycle engines, and more particularly to Rankine cycle engines using organic liquids as working substances.

2. The Prior Art Rankine cycle, high power, multistage, vapor turbines are well known as highly efficient heat engines for the production of power. Such equipment is, in general, highly complex and ill adapted to the production of compact, low weight engines of lesser power. When steam is employed, for example, it is imperative to employ multiple stages to obtain power at usable speeds, and at useful efficiency. Superheat is also essential, if wet steam is to be avoided at the turbine wheel, together with consequent handling and erosion problems.

Small (i.e., less than 1,000 hp.) engines using nozzle turbine wheel systems with associated evaporators and condensers which are suitable for mobile equipment, would preferably utilize a single stage impulse turbine. Preferably, operation should be below the critical temperature of the working fluid to minimize the pressure containment requirements. A boiling point, at atmospheric pressure, of at least 175 C. is also desirable to permit the use of a relatively small air-cooled condenser. Since the efficiency of the engine depends primarily on the temperature of the vapor at the point of expansion relative to the temperature of the condenser, a wide range between the boiling point of the liquid phase and the critical temperature of the working substance is desired. Finally, when used with rotating boilers it is highly desirable that the liquid phase have a relatively high specific gravity in order to minimize the size of boiler required to evaporate the liquid at a given rate. Rotating boilers in which the liquid working substance is contained as a layer on the heated wall of the boiler by centrifugal force are highly efficient evaporators, which provide high quality vapor. High-density liquids are particularly beneficial in such boilers since they minimize the speed of rotation required to maintain the film of liquid in the desired uniform condition. Such engines, evaporators and rotary condensers are described in more detail in the commonly assigned U.S. Pat. applications of William A. Doerner bearing Ser. Nos. 12,296 filed Feb. 18, 1970, now U.S. Pat. No. 3,590,786; 25,857 filed Apr. 6, 1970, and now abandoned; 34,455 filed May 7, 1970, and now abandoned; and 35,712 filed May 8, 1970, now U.S. Pat. No. 3,613,368.

The use of heavy fluids as working fluids for turbines has been disclosed by Tabor in U.S. Pat. No. 3,040,528 issued June 26, 1962. in that patent it is pointed out that the efflux velocity of a vapor for expansion in a turbine nozzle between two fixed temperatures is, to a first approximation inversely proportional to the square root of the molecular weight, so that by employing fluids of higher molecular weight, lower efflux velocities and hence lower turbine speeds can be achieved for a given efficiency. This patent further points out that the slope of the saturated vapor line on a temperature-entropy diagram for such liquids is positive rather than negative as in the case of steam so that an expansive superheated vapor rather than a wet vapor is obtained. The excess heat can be transferred by a heat exchanger to the condenser effluent to improve the efficiency of operation. As working fluids, Tabor suggests higher parafflns, chlorobenzene, heavier aromatics and ethers.

This invention can therefore bedefined as method of generating POW? sqmari s has? snsir siaahish wor fluid consisting of at least one compound of the formula i and R is no greater than eight is converted from liquid to vapor by heat, the vapor does work by expansion, and is thereafter condensed to liquid and recycled.

THE DRAWINGS AND DESCRIPTlON OF THE INVENTION The generation of power in a small Rankine cycle turbine using 1,3-dimethyladamantane as the working fluid is illustrated by the drawings. 1n these drawings,

FIG. 1 is a schematic view of a small Rankine cycle turbine system, and

FIG. 2 is a temperature-entropy curve for 1,3-dimethyladamantane.

Turning now to FIG. 1, the working liquid, 1,3-dimethyladamantane is evaporated in the boiler 1. The vapor passes to turbine 2 where it is expanded in the turbine nozzles and employed to run an impulse turbine. On expansion, which is essentially isentropic, the vapor becomes superheated. The exhaust from the turbine is therefore preferably passed through a heat exchanger 3, wherein the excess heat is transferred to the boiler feed. The desuperheated vapor is then passed to the condenser d where it is condensed to the liquid phase and the liquid is pumped by pump 5 back to the boiler 1 via the heat exchanger 3.

FIG. 2 shows the temperature-entropy diagram for 1,3- dimethyladamantane. The curve 10-15-14 is the saturated liquid line, the critical temperature 10 being 435 C. and the condenser temperature 14 being 139 C. at a pressure of 2.93 p.s.i.a. The recovering portion of the curve 10-11-13 is the saturated vapor line. Vapor is generated, as shown in the figures at 321 C. along lines 15-11, the boiler pressure being only 1 12 p.s.i. The vapor is transferred to the turbine and expanded in the nozzle essentially isentropically along lines 11-12, the point 12 being determined by the condenser isobar. The superheated vapor is then cooled and transferred to the liquid state partly by the regenerator and partly by the condenser.

For the above described cycle the Rankine cycle efficiency is 16 percent without regeneration and with percent heat regeneration in the heat exchanger, the Rankine cycle efficiency is 23 percent. The efflux velocity from the nozzle is 1,463 ft./sec. permitting operation at a speed of only 40,000 rpm. for a 4.5-inch diameter single: stage impulse turbine, that is, about one-half of the efflux velocity.

This invention is based on the discovery that the alkyladamantanes have surprisingly high critical temperatures in combination with suitable boiling points for the design of small, air-cooled condensers, in combination with other desirable properties which will be described hereinafter. A comparison of the physical properties of 1,3-dimethyladamantane, C T-1 TABLE 1 Physical properties of 1,3-dimethyladamantane compared with n-dodecane.

1,3-dimethyladamantane n-dodecane Mol. Wt. 164 B.P.C. 201 214.5 M.P.C. 26.5 l2 T,C. 435 385 P,p.s.i.a. 415 d. 0.90 0.75

with those of n-dodecane C T-1 is given hereinbelow in Table It will be noted that in comparison with the straight chain ndodecane, 1,3-dimethyladamantane exhibits a temperature difference between the critical temperature and the boiling point which is 635 C. greater than for n-dodecane. The 1,3- dimethyladamantane also has a substantially higher density permitting the design of more compact rotary boilers in which the liquid is held against the heated surface of the boiler by centrifugal force.

The alkyladamantanes also exhibit exceptional thermal stability in contact with the common metals of engine construction. For example, coupons of aluminum, 304 stainless steel and 1,020 ordinary cold-rolled steel were exposed in evacuated glass tubes to 1,3-dimethyladamantane at 350 C. for 107 days. The aluminum and stainless steel were unchanged while a thin blue coat formed on the 1020 steel. No degradation of the aqema n wa stvssi whe 9 1 The alkyladamantanes as a class exhibit low toxicity. For example, exposure of four rats for 4 hours to 947 parts per million of 1,3-dimethyladamantane resulted in no deaths. The rats exhibited normal we h a n aft r this. m ws,

A further advantage of alkyladamantanes for working fluids is that they have good lubricity and thus permit the use of the working flv i s s e in ri an in erases 2 Alkyladamantanes having from one to four lower alkyl bridgehead substitutents are generically useful as working fluids for Rankine cycle engines. In addition to The alkyladamantanes described above, l-methyladamantane; 1,3,5- trimethyladamantane; l-n-propyladamantane; l ,3-

diisopropyladamantane; l-n-butyladamantane; 1,3-diethyl-5- methyladamantane; 1 -pentyladamantane; 1-ethyl-3 ,5 ,7- trimethyladamantane; l,3-dimethyl-5,7-di-n-propyladamantane; l-secbutyl-3 ,S-dimethyladamantane; l-ethyl-3- propyladamantane and l-ethyl-3,5-dimethyl-7-propyladamantane are examples of alkyladamantanes which can be employed alone or in mixtures with other members of the class as working fluids.

Methods of synthesizing alkyladamantanes include those taught by Stetter et al., Chem. Ber. 92 1629 (1959); Koch and Franken, Chem. Ber. 96 213 (1963); Spengler et al., ErdSl und Kohle-Erdgas-Petrochemie 15 702 (1962); Schneider U.S. Pat. No. 3,128,316; Janoski and Moore U.S. Pat. No. 3,275,700 and Schneider U.S. Pat. No. 3,382,288.

While the use of bridgehead alkylated adamantanes have been described more particularly with reference to the generation of power with small, portable vapor turbines operating on the Rankine cycle, it will be realized that the use of these compounds is not limited to this particular application. The adamantanes with alkyl substituents at the bridgeheads are also useful with larger turbines, and with reciprocating engines which operate on the Rankine cycle.

The foregoing detailed description has been given for clarity of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious modifications will be apparent to those skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method of generating power in which a working fluid is converted from liquid to vapor by heat, said vapor is thereafter condensed to a liquid and recycled, the improvement comprising using a working fluid consisting of at least one compound of the formula 

2. The method of claim 1 in which said power is obtained by expansion of said vapor in a nozzle-turbine wheel system.
 3. The method of claim 2 in which the liquid is 1,3-dimethyladamantane.
 4. The method of claim 2 in which said liquid is heated in a rotary boiler.
 5. The method of claim 4 in which the liquid is 1,3-dimethyladamantane. 